When you plug your guitar in a mixer, it is wise to put a DI box in between.
A DI box removes the volume peaks from the signal. A mixer can break down when it is exposed to this peaks.
To be safe, one can always put a DI box in between their guitar and the amplifier, or between two effect processors for example.

The Behringer DI 100 which is tested here, has one channel. This is enough for most of the guitarists, as a guitar signal is always mono. But when you use two channels, you need two of this DI boxes.
The Behringer feels sturdy, it doesn't seem to be a problem if you happen to stand on it for example. The rubber edge protects the DI box if it falls of the stage.